Hospitals are being forced to delay operations and introduce a go-slow in treatment because of the NHS's overspending crisis, the Guardian has learned.

In London, Staffordshire and other areas forecasting big deficits, NHS commissioners are trying to save money by quietly instructing hospitals to delay non-emergency surgery until the start of the new financial year in April.

The strategy is a response to health secretary Patricia Hewitt's crackdown on overspending but it threatens the government's drive to reduce waiting times.

Hospitals are being asked to meet the government's target for a six month maximum wait - but only just. In many areas, cash-strapped primary care trusts (PCTs) are ordering consultants to introduce a five-month minimum wait unless there are medical complications.

Pressure for economies grew on Thursday when Ms Hewitt ordered budgetary hit squads into the most financially overstretched NHS trusts in an attempt to cut deficits worth £948m across England. But yesterday it emerged NHS commissioners were already starting to squeeze budgets by offering a poorer service to patients.

The Guardian has learned that:

· The University Hospital of North Staffordshire, in Stoke-on-Trent, has been told it must stop operating on women needing gynaecological treatment who had been on its waiting list for only two months. The PCTs said they would refuse to pay for the work unless the women were kept waiting for nearly six months - the government's target maximum. By delaying treatment, spending is postponed into the next financial year.

A spokesman said the hospital sent letters to 528 patients this week cancelling bookings for operations before March 31 and offering appointments in the new financial year.

· In London, Hammersmith and Fulham PCT has agreed a business plan that also slows down treatment. "The risk in this area continues to be the treatment of patients faster than is required by the targets and therefore at greater expense than our funding," the plan says. To reduce this risk, we are requiring the main acute trusts to treat non-urgent elective patients within an average of five months." A spokesman for North West Thames strategic health authority said the PCT's policy is in line with other trusts in London.

· Within the last few days, East Suffolk PCT has been ordered by its health authority to abandon an attempt to delay paying its March salary cheques to contain its overspend. The trust said last month that it would no longer provide hip replacements to obese patients, partly due to financial pressures.

Peter Blythin, chief executive of North Staffordshire hospital, said: "The PCTs have asked us not to treat any of their patients whose surgery was due to go ahead sooner than the target. We are not happy as we were trying to drive the lists down ready for the 2008 target that people should wait no longer than 18 weeks from seeing the GP to having their operation."

The pressure to delay operations came as Ms Hewitt was celebrating an October waiting list figure of 792,000 - the lowest since data was first collected in this way in September 1988. She said: "The service is on target to achieve a maximum wait of six months for an operation by the end of this year and we know that most patients are already being treated much quicker."

The Department of Health was asked if delaying patients' treatment was a suitable method for avoiding an overspend. A spokesman said: "This is an operational issue for the local NHS. Most patients wait less than six months: the average wait for [planned] treatment is nine weeks."